1. Field of the Invention
This invention relates to overload protection circuits and, more particularly, to lightning protection for transmission line repeaters.
2. Description of the Prior Art
Transmission line repeaters are located at spaced positions along a transmission line and serve the function of amplifying communication signals transmitted in either or both directions along the transmission line. Such repeaters are made up of electronic components which might become seriously damaged by exposure to excessive voltages caused, for example, by lightning strikes on the transmission line. Since such transmission lines are often exposed to the elements, the probability of a damaging lightning strike is reasonably high during the lifetime of the repeater.
It is therefore common to protect such repeaters by means of voltage breakdown devices which respond to excessive voltages by creating a temporary short circuit between the transmission line and ground potential. Current surges are thereby deflected to ground and do not harm the electrical components of the repeater.
In order to permit deflection of current surges to ground, a high current capacity ground connection must be provided at each repeater location to accommodate the shunted current. Such ground connections can be difficult and expensive to provide for repeaters on some types of transmission lines, such as aerial cables, where a ground connection is not immediately available.